Effects of an IgE receptor polymorphism acting on immunity, susceptibility to infection and reproduction in a wild rodent

The genotype of an individual is an important predictor of their immune function, and subsequently, their ability to control or avoid infection and ultimately contribute offspring to the next generation. However, the same genotype, subjected to different intrinsic and/or extrinsic environments can also result in different phenotypic outcomes, which can be missed in controlled laboratory studies. Natural wildlife populations, which capture both genotypic and environmental variability, provide an opportunity to more fully understand the phenotypic expression of genetic variation. We identified a synonymous polymorphism in the high-affinity Immunoglobulin E (IgE) receptor (GC and non-GC haplotypes) that has sex-dependent effects on immune gene expression, susceptibility to infection and reproductive success of individuals in a natural population of field voles (Microtus agrestis). We found that the effect of the GC haplotype on the expression of immune genes differed between sexes. While males with the GC haplotype had upregulated more pro-inflammatory genes, including the cytokine Il33, females had upregulated more anti-inflammatory genes, including the cytokine inhibitor Socs3. Furthermore we found an effect of the GC haplotype on the probability of infection with a common microparasite, Babesia microti, in females - with females carrying the GC haplotype being more likely to be infected. Finally, we found an effect of the GC haplotype on reproductive success in males - with males carrying the GC haplotype having a lower reproductive success. This is a rare example of a polymorphism whose consequences we are able to follow across immunity, infection and reproduction for both males and females in a natural population.